Tests
and Diagnostics

Procedures
Used to Diagnose CRF

What
is Normal?

It
was surprisingly difficult to find normal values for
Heart Rate and Blood Pressure. Different authorities
cite different normals. We used an average of the values
cited.

White
Coat Syndrome

Cats are much better survival machines than they are
patients. In a vet's office, a cat's respiration, heart
rate and blood pressure may all be elevated as the cat
goes into 'fight or flight' preparation mode when put
in an unfamiliar or stressful situation.

Ask
your veterinarian to do a major renal panel if you think your
cat has CRF symptoms. If your cat is age seven or older, have
your veterinarian check for CRF during the cat's annual exams.
A Complete Blood Count (CBC) examines red and white blood
cells and a Blood Chemistry Test checks electrolytes, BUN,
creatinine, cholesterol, glucose, liver enzymes, etc. Together,
these two tests, along with a urinalysis, will provide enough
information for the veterinarian to determine if your cat
is in CRF.

Creatinine and BUN are the two most important elements of
the blood test for cats with CRF. When these are elevated
and the urine is dilute, there is a very real possibility
that the cat is in CRF. When the creatinine and BUN are elevated,
it is likely that approximately 70% of kidney function is
already gone. Since low normal potassium levels, dental disease
and high blood pressure are now suspected to be linked to
the development of CRF, it is advisable to have these conditions
checked, too.

Lab
Results

While
lab results are certainly indicative of the progression of
CRF, it must be remembered that there can be variations on
blood tests - different labs can produce somewhat different
results from the same samples because of standards and testing
methodology. The manner in which the blood was taken may affect
the results of blood work testing. How gentle the technician
is, from what vein the blood is taken and what size the needle
is can all have an effect on test results. Whether or not
the animal is severely stressed can affect the results as
can when and what the cat ate and when the cat was last hydrated.
In some cases, drugs given to a cat within proximity of taking
blood can affect results. What is normal for one cat may not
be normal for another. You look for trends and then at the
long-term trend. We have found, after becoming frantic over
lab results, that how the cat is acting is equally important.
A friend of ours, who took care of a CRF cat for several years,
gave us this valuable advice - "Treat the cat, not the lab
work". Blood tests are just one piece (albeit a very valuable
one) of the diagnostic puzzle.

Always
request copies of the lab report from your veterinarian. From
this information, a chart or spreadsheet can be created to
record results of each blood test. From this chart, you and
your veterinarian will be able to see the entire history at
a glance. Become familiar with the normal limits for various
blood values. These numbers are usually given on the lab report
and may vary slightly from lab to lab.

How
Often Should Blood Tests be Done?

Having
blood drawn is very stressful for a cat and its caregiver(s).
It takes a while to replenish even what seems like a small
amount of blood and unless there is a discernible rapid downward
trend or there are clinical symptoms of a problem or a worsening
of the cat's condition, think twice before having frequent
blood work done. If you get two blood tests in a row that
are pretty close in the values there is no need to put the
cat through the stress every month. The negative effects of
the stress could offset anything to be gained from the more
frequent lab work. Also, the more often you take blood, the
tougher the cat's veins and skin will become. Later on, as
the disease progresses and you need to take more frequent
blood samples, it will be difficult to find a good site to
insert the needle because of the scar tissue. When you do
have blood tests done, request complete panels in order to
benefit from as much information as possible. If your cat
doesn't cooperate with jugular sampling, it may be easier
and less stressful to take blood from a leg. You may reach
a point when both you and your veterinarian feel that additional
blood tests won't serve any useful purpose.

If
your cat is anemic, the value of periodic blood panels may
be outweighed by the risk of drawing blood that is not easily
replaced.

Obviously,
the interpretation of blood tests and urinalysis can only
be done by a veterinarian. However, the following minimal
information may be helpful in your understanding of what all
those numbers and words on the lab report mean.

Blood
Tests

Common
Tested Blood Values Relevant to CRF Cats

Amylase

Some
vets feel that slightly elevated Amylase levels
can sometimes be a pre-cursor to CRF before
other symptoms occur.

BUN
(blood urea nitrogen)

BUN
is a waste product excreted through the kidneys.
BUN is more reflective of dietary impacts than
creatinine. An increase in BUN can also be due
to dehydration (a symptom of CRF and many other
diseases and syndromes).

Cholesterol

Increases
in cholesterol levels may occur with kidney disease.

Creatinine

Creatinine
is a waste product excreted through the kidneys.
It is indicative of overall declining kidney
function.

Calcium

A
healthy cat will have a calcium to phosphorus
ratio of 1:1 to 2:1. Since damaged kidneys cannot
adequately process phosphorus, calcium levels
must rise to compensate.

PCV
(Packed Cell Volume) or HCT (hematocrit)

This
number is watched carefully as it is indicative
of anemia which is common in CRF cats. In this
test the blood sample is centrifuged to separate
the blood cells from the fluid portion (serum)
of the blood. The volume of the cells is measured
as a percentage of the total sample. Normally,
40% of the cat's blood consists of cells and
the rest is liquid.

Phosphorus

During
CRF, high levels of phosphorus accumulate in
the blood (hyperphosphatemia) because the kidneys
can no longer efficiently excrete it. Excess
phosphorus intake can make CRF worse. Phosphorus
levels should be monitored on a regular basis.

Potassium

Potassium
levels are critical in CRF cats and should be
regularly monitored. Potassium loss can result
from frequent vomiting and in urination. Sub-Q
therapy may also dilute potassium even further.
Low potassium is called hypokalemia. Even if
your cat's potassium is in the low normal range,
it may be necessary to give him a potassium
supplement. This is because with CRF, critical
stored potassium in the tissues is used, often
making the blood analysis appear normal.

Sodium

Sodium
should be monitored closely as the kidneys of
CRF cats are unable to excrete sufficient quantities
of it. This may result in hypertension.

Special
Blood Tests

Blood
gases

Blood
gases are normally checked by a specialist as
regular veterinarians usually do not have the
facilities for this type of testing. The specialist
may either have the capability to test in-house
or will use a local hospital for testing. If
blood gases aren't normal, it is usually possible
to make adjustments with medications.

Parathyroid
hormone test

This
test is done to determine if the cat is a candidate
for Calcitriol.

Reticulocyte
Count

This
test is an accurate measurement of the production
of new red blood cells. CRF cats tend to become
anemic and a retic count will tell you how effectively
and at what rate new red blood cells are being
pumped out of the bone marrow. The retic count
will really become significant if the red blood
count goes down.

T-4
test

Hyperthyroidism,
an abnormal increase in the production of the
thyroid's hormones, is a very common problem
in older cats and occasional T-4 tests should
be done.

Urinalysis

Urinalysis
is a series of chemical and physical tests, the results
of which indicate the specific gravity and pH of the
sample and the presence and level of blood, glucose
and other components of the sample. Since the major
CRF data comes from blood tests, it's not necessary
to have urine tests done quite as often.

Specific
gravity is an important measure of how well the
urine is being concentrated by the cat's kidneys,
and therefore, how well the kidneys are actually functioning
as filters. CRF cats cannot adequately concentrate
urine so a low specific gravity is indicative of renal
failure. The normal range for specific gravity is
between 1.015 and 1.060 but only concentrations higher
than about 1.030 can be considered solid evidence
of normal kidney function.

Urine Culture and Sensitivity

It is a good idea to have a urine culture and sensitivity test done at the same time as the urinalysis, particularly if bacteria is detected in the sample.Renal failure can sometimes be a result of a kidney infection.If an infection is present, the culture and sensitivity test will show what type of bacteria is present and allow the vet to treat it with specific antibiotics.

Urine
Protein Creatinine (Urine P:C) Ratio A test distributed by IDEXX Laboratories allows
veterinarians who have an IDEXX VetTest Chemistry
Analyzer to measure Proteinurea and Creatinine from
urine samples and use the measurements to calculate
the ratio of creatinine to protein. The manufacturer
says that the Urine P:C ratio can be used to diagnose
CRF much earlier than the currently used testing methods
and that the ratio of protein to creatinine is indicative
of the seriousness of the disease which would permit
the veterinarian to make a more accurate prognosis.For additional information, please visit the IDEXX Laboratories website.

E.R.D.
HealthScreen Feline Urine TestA
urine test (E.R.D. HealthScreen Feline Urine Test)
has been developed by Heska to detect the presence
of microalbuminuria (small amounts of albumin) in
feline urine. The presence of albumin in the urine
is an indicator of glomerular damage associated with
renal failure and/or other underlying conditions causing
albumin to leak into the urine. This tool is the only
test that will detect albumin leakage and may provide
an early diagnosis of kidney damage long before
conventional BUN and Creatinine become elevated. For
additional information, please visit Heska’s website.

Two
common ways of taking urine samples at the veterinarian's
office are cystocentesis (a very thin needle is
inserted through the skin into the bladder and
an uncontaminated urine sample is obtained) and
by expression, in which the veterinarian puts
external pressure on the bladder causing the cat
to urinate. Cystocentesis is the most accurate,
cleanest way of obtaining a urine sample and is
probably less painful for the cat than the expression
method.

If
you are not comfortable with the methods listed
above, you might consider taking the urine sample
at home. If your cat will cooperate, you may
be able to use the free catch method. Hold a
sterile plastic container under the cat when
it urinates. A second method is done with plastic
pellets. Check with your veterinarian to see
if you can obtain this product. Many cats will
use the litter box with these pellets rather
than litter. After the cat has urinated, drain
the urine from the litter box into a jar. If
your cat will urinate in an empty litter box,
this is yet another alternative. With all of
these home methods, the urine must be refrigerated
until you can take it to the veterinarian's
office (this must be done within a few hours)
and there will probably be bacteria included
with the sample, from the litter box and from
the external cat.

Recently (2007), a product called the Smart Cat Box has become available. This unique type of litter box enables the caregiver to easily collect a urine sample for testing.

Other
Procedures

Biopsy

A
biopsy is the most certain method of obtaining
direct evidence of the state of the kidneys.
However, biopsies can be somewhat dangerous
procedures and may not add much to the diagnostic
picture. If a biopsy is to be done, have a blood
clotting profile(or coagulation test) done beforehand.
Sedation or anesthetic may be required. Be sure
there is a blood source for transfusion in case
of unexpected bleeding during the biopsy procedure.

Blood PressureBlood
pressure can be checked as a means to find
out if hypertension is present. Some veterinarians
do not have the equipment or specialized training
to take blood pressure but it is becoming
a routine test for CRF cats. A veterinary
specialist may need to be consulted to perform
blood pressure monitoring.

GFR
Testing - Iohexol Clearance Test

Unlike BUN and serum creatinine tests which
do not register deterioration of kidney function
until 70% or more of nephrons are non-functional,
the GFR (Glomerular Filtration Rate) test is
directly related to the functional renal mass
and thus can give a much earlier indication
of renal failure. There is currently no recommended
protocol for using the GFR test on a routine
basis in healthy animals. The value of early
detection, however, increases as drug and other
therapeutic measures are improved. This suggests
that the test may be of some positive benefit
as an adjunct to an annual physical for adult
cats.

Essentially, the GFR test measures the rate
at which the kidneys clear a tagged substance
from the system. While the clearance rate of
creatinine or insulin can be used, the new standard
for GFR testing is iohexol. Iohexol is a radiographic
substance developed for use in many diagnostic
procedures. It is entirely excreted by the kidneys
through the process of glomerular filtration.
Measuring the amount remaining in the system
at carefully measured intervals can give an
accurate measure of the mass of functioning
kidney tissue.

The test is performed by administering a single
intravenous dose of iohexol at 300mg/kg. The
time of the administration is recorded to the
nearest minute. Three to four ml blood samples
are then drawn two, three and four hours after
the administration. The samples are labeled
with the owner's name, animal I.D. and time
of sampling. The blood is allowed to clot and
the serum samples are transferred to plastic
vials labeled with the exact sampling time.
The samples are chilled and shipped to the testing
laboratory where the concentration of iohexol
will be measured. By extension, these measurements
will be used to calculate the functioning kidney
mass.

Ultrasound

An
ultrasound will tell you the condition of the
cat's kidneys (whether normal or shrunken) and
will give you a baseline for the future. Ultrasounds
are certainly not stress-free for the cat, but
they are non-invasive, rarely require sedation
or an anesthetic to perform the procedure and
there is no radiation danger. Your cat's fur
will be shaved in the area where the ultrasound
is being done. Not all veterinary offices are
equipped to do ultrasound testing and you may
be referred to another facility.

Note
- An ultrasound was the only reliable test
for early detection of PKD (Polycystic Kidney
Disease) in cats until just recently. UC
Davis has identified the
gene mutation that causes PKD and now it
can be detected with nearly 100 percent
accuracy.

SDMAScience Dailyreports that a new biomarker called 'SDMA' has been developed that can provide earlier identification of chronic kidney disease in cats. As of December 1, 2014, the test is not yet commericially available.